FIG. 1 is a front perspective view of a prior art bumper plate 100. A bumper plate is a disk shaped weight that is mounted on a bar bell for weight training. The bumper plate comprises an outer rim 102, body 104, hub 106 and collar 108. The collar describes a central bar hole 110. The interface between the rim and body comprises an undercut 114. Thus the thickness of the body may be somewhat less than the thickness of the rim. The interface between the body and the hub comprises a step 116. Thus the hub may have a larger thickness than the body. The larger thicknesses of the rim and hub relative to the body allow for raised indicia 120 to be molded into the body. The hub and rim protect said indicia when the bumper plate lies flat on the ground. The undercut also acts as a handle to make it easier to lift the bumper plate. The outer edge of the rim comprises a bevel 112. This makes it easier to pick up the bumper plate when it is lying flat on the ground.
A typical bumper plate may have a radius 122 in the range of 8.75 inches to 8.86 inches. 8.86 inches is a standard size for competition. The bar hole radius 126 is about 1 inch. The hub radius 124 is about 4.26 inches. The rim height 132 is about 1.77 inches. The undercut is about 0.43 inches. The rim thickness 136 may be in the range of 1.4 inches to 3.75 inches depending upon the weight of the bumper plate.
The bumper plate may be made of solid rubber, bonded crumb rubber, polyurethane or other elastomer. The durometer of the elastomer may be in the range of 70 to 90. The collar may be made of metal. The hub may comprise a metal disk plate for extra weight.
One of the drawbacks of the prior art bumper plate design is that there is a tradeoff between the noise made when the bumper plates are dropped on the floor and the amount of bounce in the bumper plates after they hit the floor. Low durometer elastomers (e.g. 70) are relatively quiet, but they have a high bounce which can lead to injury. High durometer elastomers (e.g. 90) have a low bounce, but can make a very loud noise when dropped. Thus there is a long felt need for a bumper plate design that has both low bounce and low noise when dropped.